package com.yc.testparm;

import java.lang.reflect.Field;
import sun.misc.Unsafe;

/**
 * Java不能直接访问操作系统底层，而是通过本地方法来访问。
 * Unsafe类提供了硬件级别的原子操作,在java中内存中的对象地址是可变的，所以获得的内存地址有可能会变化。
 * 要获得内存地址也只能通过Unsafe的方法来获得,下面类提供了获取java对象内存地址的方法
 * @author yuancan
 *
 */
public class Addresser {
	String a = "c";
	private static Unsafe unsafe;

	static {
		try {
			Field field = Unsafe.class.getDeclaredField("theUnsafe");
			field.setAccessible(true);
			unsafe = (Unsafe) field.get(null);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public static long addressOf(Object o) throws Exception {

		Object[] array = new Object[] { o };

		long baseOffset = unsafe.arrayBaseOffset(Object[].class);
		// arrayBaseOffset方法是一个本地方法，可以获取数组第一个元素的偏移地址
		int addressSize = unsafe.addressSize();
		long objectAddress;
		switch (addressSize) {
		case 4:
			objectAddress = unsafe.getInt(array, baseOffset);
			// getInt方法获取对象中offset偏移地址对应的int型field的值
			break;
		case 8:
			objectAddress = unsafe.getLong(array, baseOffset);
			// getLong方法获取对象中offset偏移地址对应的long型field的值
			break;
		default:
			throw new Error("unsupported address size: " + addressSize);
		}
		return (objectAddress);
	}

	public static void main(String... args) throws Exception {
		Object mine = "Hello world".toCharArray(); // 先把字符串转化为数组对象
		String aa = "aa";
		String aa1 = "a" + "a";
		long address = addressOf(aa);
		long address1 = addressOf(aa1);
//		long address = addressOf(mine);
		System.out.println("Addess: " + address);
		System.out.println("Addess: " + address1);

		// Verify address works - should see the characters in the array in the output
//		printBytes(address, 27);
	}

	public static void printBytes(long objectAddress, int num) {
		for (long i = 0; i < num; i++) {
			int cur = unsafe.getByte(objectAddress + i);
			System.out.print((char) cur);
		}
		System.out.println();
	}
}